1. Field
The present invention relates generally to radio frequency processing systems and methods, including mixers and methods for downconverting to intermediate frequency. The systems and methods may be employed in telecommunications, including uses in cellular telephone receivers and in global positioning system (GPS) receivers.
2. Background
A modern communication system is expected to provide reliable data transmission for a variety of applications, such as voice and data applications. In a point-to-multipoint communications context, known communication systems are based on frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and perhaps other multiple access communication schemes.
A CDMA system may be designed to support one or more CDMA standards, such as (1) the “TIA/EIA-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (this standard with its enhanced revisions A and B may be referred to as the “IS-95 standard”), (2) the “TIA/EIA-98-C Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Station” (the “IS-98 standard”), (3) the standard sponsored by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents known as the “W-CDMA standard,” (4) the standard sponsored by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “TIA/EIA/IS-856 cdma2000 High Rate Packet Data Air Interface Specification” (the “cdma2000 standard” collectively), (5) the 1xEV-DO standard, and (6) certain other standards. The standards expressly listed above are incorporated by reference as if fully set forth herein, including annexes, appendices, and other attachments.
It is desirable and sometimes required for a provider of communication services to know the geographic location of the serviced telephones and other user equipment devices. For example, the geographic location may need to be known in order to identify the location to operators responding to emergency telephone calls (e.g., 911 calls in the U.S. and 112 in certain European locales). The U.S. Federal Communications Commission (FCC), for example, mandates Enhanced 911 (E911) services. Knowledge of the geographic location may also be desired to provide users of cellular communication devices with navigational and other location-specific services and advertising. For this reason, many cellular communication devices are equipped with GPS receivers.
Both GPS receivers and cellular system receivers generally include mixers and related devices for converting the received radio frequency signals to a lower frequency, for subsequent processing at that lower frequency. The lower frequency may be an intermediate frequency of the cellular receiver, or an intermediate frequency of a GPS receiver.
A number of sometime competing criteria affect the design of communication devices, such as the cellular and GPS receivers mentioned above. The criteria include size, weight, power consumption, and noise figure. Therefore, there is a need in the art for radio frequency mixing apparatus with improved noise figures. There is also a need in the art for mixing apparatus with reduced size and reduced weight. There is a further need in the art for mixing apparatus with reduced power consumption.